1. Field of the Invention
The present invention relates to an apparatus, a method, and a computer-readable recording medium for performing a color material saving process.
2. Description of the Related Art
In image forming apparatuses that form images using color material such as toner or ink, there is known an image forming apparatus having not only a normal outputting mode for outputting images using a normal amount of color material but also a color material saving mode for outputting images using a reduced amount of color material. As for color material saving methods used in the color material saving mode, there are, for example, a method of converting the data of each pixel to low density pixels or a method of skipping pixels (pixel skipping). However, since the images output by using these methods have their density reduced, image quality is degraded. In a case of forming character images (text images), the characters (text) may be hardly legible depending on the degree of the degradation of image quality.
In order to prevent this problem of illegible characters, there is a color material saving process where an edge part(s) of a character image is detected and a lesser amount of color material is saved for forming the edge part than that for forming a non-edge part of the character image. By using this process, the edge part of the character image can be emphasized to reduce the illegibility of the character image. However, because this color material saving process detects not only the edges of a character image but also sharp edges of a photograph image, a lesser amount of color material is saved for forming the edge part than that for forming a non-edge part of the photograph image. Therefore, in a case where the color material saving process is performed on an image having a character image and a photograph image mixed together, image quality is degraded due to undesired emphasis at the edge parts of a plotting target.
Japanese Laid-Open Patent Publication No. 11-151833 discloses a printer configured to recognize a character area and a photograph area of an original image received from a computer or the like and apply different color material saving processes to the character area and the photograph area. With this configuration, a color material saving process that emphasizes the edge parts can be applied to the character area of the original image for improving legibility while another color material saving process that uses an evenly reduced amount of color material can be applied to the photograph area of the original image for preventing image degradation due to undesired emphasis of the edge parts. Although this configuration can appropriately and speedily recognize a character area and a photograph area of an original image in a case where the data of the original image contain plotting commands such as Page Description Language (PDL), this configuration cannot recognize the character area and the photograph area in a case where the data of the original data contain only image data (e.g., bit map image data).
Japanese Laid-Open Patent Publication No. 2005-234391 discloses a copier configured to recognize a character area and a photograph area of an original image containing only image data. This configuration obtains information from the original image containing only image data by scanning a document on which the original image is formed and analyzes image features of the original image. Based on a result of the analysis, the character area and the photograph area of the original image can be recognized. Accordingly, a color material saving process for emphasizing edge parts can be applied to the character area while another color material saving process for evenly using a reduced amount of color material can be applied to the photograph area.
However, Japanese Laid-Open Patent Publication No. 2005-234391 does not specifically disclose a method of how to recognize a character area and a photograph area of an original image according to the result of analyzing image features of the original image. Even by combining other related technologies, it is difficult to precisely recognize a character area and a photograph area of an original image containing only image data. It is particularly difficult for recognizing the character area and the photograph area in a case where a photograph image is formed in the background of a character image. In this case, such a mixed area having the photograph image in the background of the character image is likely to be erroneously recognized as a photograph area. When such an error occurs, the edge parts of the characters in the mixed area cannot be enhanced and the legibility of the characters is degraded.